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Chapter 6 Cellular Respiration: Obtaining Energy from Food PowerPoint® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko © 2010 Pearson Education, Inc. • Plant and animal cells perform cellular respiration, a chemical process that: – Primarily occurs in mitochondria – Harvests energy stored in organic molecules – Uses oxygen – Generates ATP © 2010 Pearson Education, Inc. • The waste products of cellular respiration are: – CO2 and H2O – Used in photosynthesis • Animals perform only cellular respiration. • Plants perform: – Photosynthesis and – Cellular respiration © 2010 Pearson Education, Inc. Study the relationship of photosynthesis & cell respiration C6H12O6 Sunlight energy enters ecosystem Photosynthesis CO2 Glucose Carbon dioxide O2 Oxygen H2O Water Cellular respiration ATP drives cellular work Heat energy exits ecosystem Figure 6.2 CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY • Cellular respiration is: – The main way that chemical energy is harvested from food and converted to ATP – An aerobic process—it requires oxygen • Cellular respiration and breathing are closely related. – Cellular respiration requires a cell to exchange gases with its surroundings. – Cells take in oxygen gas. – Cells release waste carbon dioxide gas. – Breathing exchanges these same gases between the blood and outside air. © 2010 Pearson Education, Inc. O2 CO2 Breathing Lungs CO2 O2 Cellular respiration Muscle cells Figure 6.3a The overall equation for what happens to glucose during cellular respiration: Oxidation Glucose loses electrons (and hydrogens) C6H12O6 Glucose 6 O2 Oxygen 6 CO2 Carbon dioxide 6 H 2O Water Reduction Oxygen gains electrons (and hydrogens) Figure 6.UN02 The Role of Oxygen in Cellular Respiration • Cellular respiration can produce up to 38 ATP molecules for each glucose molecule consumed. • During cellular respiration, hydrogen and its bonding electrons change partners. – Hydrogen and its electrons go from sugar to oxygen, forming water. – This hydrogen transfer is why oxygen is so vital to cellular respiration. © 2010 Pearson Education, Inc. An Overview of Cellular Respiration • Cellular respiration: – Is an example of a metabolic pathway, which is a series of chemical reactions in cells • All of the reactions involved in cellular respiration can be grouped into three main stages: – Glycolysis – The citric acid cycle – Electron transport © 2010 Pearson Education, Inc. Cytoplasm Mitochondrion High-energy electrons carried by NADH Glycolysis Glucose 2 Pyruvic acid ATP High-energy electrons carried mainly by NADH Citric Acid Cycle Electron Transport ATP ATP Figure 6.6a Stage 1: Glycolysis • A six-carbon glucose molecule is split in half to form two molecules of pyruvic acid. • These two molecules then donate high energy electrons to NAD+, forming NADH. – Uses two ATP molecules per glucose to split the six-carbon glucose – Makes four additional ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP • Thus, glycolysis produces a net of two molecules of ATP per glucose molecule. © 2010 Pearson Education, Inc. Stage 2: The Citric Acid Cycle • The citric acid cycle completes the breakdown of sugar. • The citric acid cycle: – Extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2 – Uses some of this energy to make ATP – Forms NADH and FADH2 © 2010 Pearson Education, Inc. INPUT OUTPUT Citric acid Acetic acid 2 CO2 ADP P ATP Citric Acid Cycle 3 NAD 3 FAD NADH FADH2 Acceptor molecule Figure 6.10 INPUT OUTPUT Oxidation of the fuel generates NADH (from glycolysis) NAD (to citric acid cycle) NADH CoA Pyruvic acid Pyruvic acid loses a carbon as CO2 Acetic acid CO2 Coenzyme A Acetic acid attaches to coenzyme A Acetyl CoA Figure 6.9 Stage 3: Electron Transport • The molecules of the electron transport chain are built into the inner membranes of mitochondria. – The chain functions as a chemical machine that uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane. – These ions store potential energy. • When the hydrogen ions flow back through the membrane, they release energy. – The hydrogen ions flow through ATP synthase. – ATP synthase: – Takes the energy from this flow – Synthesizes ATP © 2010 Pearson Education, Inc. Space between H membranes Electron carrier Protein complex H H H H H FADH2 FAD H H H H H H H Inner mitochondrial membrane Electron flow 1 2 NADH H Matrix H NAD H O2 2 H H2O ADP P H Electron transport chain H ATP H ATP synthase Figure 6.11a Cytoplasm Mitochondrion 2 NADH Glycolysis Glucose 2 Pyruvic acid 2 NADH 2 Acetyl CoA 6 NADH 2 FADH2 Citric Acid Cycle 2 ATP 2 ATP by direct synthesis by direct synthesis Electron Transport Maximum per glucose: About 34 ATP About 38 ATP by ATP synthase Figure 6.13 • Cyanide is a deadly poison that: – Binds to one of the protein complexes in the electron transport chain – Prevents the passage of electrons to oxygen – Stops the production of ATP © 2010 Pearson Education, Inc. The Versatility of Cellular Respiration • In addition to glucose, cellular respiration can “burn”: – Diverse types of carbohydrates – Fats – Proteins © 2010 Pearson Education, Inc. FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY • Some of your cells can actually work for short periods without oxygen. • Fermentation is the anaerobic (without oxygen) harvest of food energy. • After functioning anaerobically for about 15 seconds: – Muscle cells will begin to generate ATP by the process of fermentation • Fermentation relies on glycolysis to produce ATP. • In human muscle cells, lactic acid is a by-product. © 2010 Pearson Education, Inc. INPUT 2 ADP 2 P OUTPUT 2 ATP Glycolysis 2 NAD 2 NADH Glucose 2 NADH 2 NAD 2 Pyruvic 2 H acid 2 Lactic acid Figure 6.14 • Yeast are a type of microscopic fungus that: – Use a different type of fermentation – Produce CO2 and ethyl alcohol instead of lactic acid • This type of fermentation, called alcoholic fermentation, is used to produce: – Beer – Wine – Breads © 2010 Pearson Education, Inc. INPUT 2 ADP 2 P OUTPUT 2 ATP 2 CO2 released Glycolysis 2 NAD 2 NADH Glucose 2 NADH 2 NAD 2 Pyruvic 2 H acid 2 Ethyl alcohol Bread with air bubbles produced by fermenting yeast Beer fermentation Figure 6.16